Answered by Alex Beam:
Here I can only speculate, and say: very little. Nursing, not unlike primary and secondary school teaching, isn't particularly well paid. Psychiatric nursing is not the most highly paid specialty, nor for that matter the most desirable. I have friends in nurses' unions, but I'm not aware of any of the major mental hospitals here (in the Boston area) having a unionized staff.
Social workers, generally speaking, are even less well paid. And, as I wrote to a previous questioner, money is moving OUT of mental health services right now, not in. So I don't see too much cause for hope in the future.